A lighting unit including an LED light source and a plate-like lens body used in combination has conventionally been suggested (see, for example, Japanese Patent No. 4458359 which is hereinafter called patent literature 1).
As shown in FIGS. 1A to 1C, a lighting unit 200 disclosed in Patent Literature 1 can include a plate-like lens body 210, and an LED light source 220 arranged to face the front surface of the lens body 210. The lens body 210 can have a first side surface 211 functioning as a light exiting surface having a substantially rectangular shape greater in width than in thickness, and a second side surface 212 opposite the first side surface 211.
In the lighting unit 200 of the aforementioned structure, the lens body 210 with an optical element for causing refraction or reflection can allow the first side surface 211 as a light exiting surface to form a linear light source for emitting linear light. However, arrangement of an optical axis AX1 of the lens body 210 and an optical axis AX2 of the LED light source 220 crossing each other at right angles (see FIG. 1B) can make the layout design of a lamp difficult.
Alternatively, a linear light source for emitting linear light may also be formed by placing the LED light source 220 to face a side surface of the lens body 210 and not the front surface of the lens body 210 as shown in FIG. 2.
In this structure, however, a thickness H of the lens body 210 should be increased in order to increase the area of a light incident surface with the intention of enhancing the efficiency of use of light emitted from the LED light source 220. This makes the lens body 210 have a greater thickness accordingly, making it difficult or impossible to realize weight saving of the lighting unit 200.